This winter opened with bitter cold for much of the nation, including parts of the country not used to snow and ice. Here in the northern tier states we are at least equipped to respond to winter storms, but they always pose a challenge.

At a very human level, cold temperatures often show up first as the experience of cold hands and cold feet. Even with good socks and sturdy boots, when I’m outside there are temperatures below which I cannot keep my toes warm (this is more common the older I get, a trend I don’t appreciate).

There are two basic ways to combat freezing toes – and both depend on the chemical miracle of how oxygen (my favorite element) interacts with so much of the world around us.

The first approach to warming up, of course, is simply to build a fire. Fire, from a chemist’s point of view, is a rapid chemical reaction of oxygen with carbon-rich materials. Where I walk my dog on cold Sunday afternoons in the winter, along the seemingly endless Snake River, fishermen pursuing salmon and steelhead use driftwood to build fires. With plenty of fuel available, the fires can be big.

If I stop and talk a bit with the fishermen, I can sidle up to the fires and warm myself at least a small bit. But the cost of that warmth – and let me emphasize this for the urban reader – is smelling like the stench of a fishy bonfire for the rest of the day, of having clothes and a coat that smell like that fish-gut fire until they are all fully laundered.

It’s not a small matter, at least not for us girls.

Enter the miracle of the modern toe and finger warmer based on a more controlled chemical reaction between oxygen and iron — with iron functioning like the carbon in wood-fires.

“Toe warmers” are small and thin devices that have adhesive on the back. You open the package that they come in from the store, stick a pair on your socks above or below your toes, put on your boots, and soak up the blessings of a trickle of heat on your 10 little piggies all day long.

How can toe warmers possibly work?

First, it’s important to note the bags they come in are fully airtight. When you take them out, they are exposed to oxygen — because the air around us is 20 percent oxygen.

So far, so good.

The active ingredient in the toe warmers is iron. It’s not a chunk of iron, obviously, but a fine powder of iron filings, spread out in the toe warmer. The finely divided iron means it’s more likely to chemically react and interact with molecules around it — not just sit there in unchanging stubbornness like some middle-aged geologists.

Iron reacts with oxygen in a similar way as carbon, going through the process of oxidation. Iron plus oxygen creates iron oxide, also known as rust, also known as the main material on the underside of my ’87 pickup. When iron and oxygen create rust, heat is released. That’s the fundamental key to the toe warmers.

There are a variety of other hand-warming devices, too, that run on different principles and can fit in your mittens. But the little pouches of iron-filings are my personal favorite because they are so thin they fit in my boots below my toes. In my (ever so slightly stinky) boots, my toe warmers are a small pad that’s about 100 degrees F or a little warmer (according to my measurements). That’s blessedly cozy for my 10 toes on a cold afternoon.

The iron-filing toe-warmers are one-use-only. That’s a shame, but it happens because there’s no chemically easy way to pull the oxygen atoms off the iron once the two have combined. So you toss out the toe-warmers when their heat dies down to nil.

But, on the bright side, you and your clothes don’t smell like a fishy fire for the rest of the day.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the Web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Sciences at Washington State University.